There has so far been used a picture display system, termed a multi-window system, configured for demonstrating user interfaces of plural applications on a single display. This multi-window system is a client-server system, composed of applications for generating plural pictures and a picture server for synthesizing the pictures generated by the applications.
Among the multi-window systems, so far proposed, there is such a system in which, in case the necessity arises for re-rendering a picture within an application, a full virtual picture is re-rendered on the application, and a full virtual picture on the picture server is re-rendered with picture data of a re-rendered area to update the demonstration of a real picture surface, as disclosed in Japanese Laid-Open Patent Publication JP-A-6-250640.
This known multi-window system suffers from a drawback that, in case a window is re-rendered in an picture surface where plural applications have been displayed, it is necessary for the totality of the applications, displayed on the viewing surface, to carry out the window re-rendering, with the result that the re-rendering load increases with increase in the number of times of booting the applications.